skip mongodb on HHVM

tests/unit/data/travis/mongodb-setup.sh

@@ -4,7 +4,11 @@
 
 mongod --version
 
-echo "extension = mongo.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini
+if (php --version | grep -i HipHop > /dev/null); then
+  echo "mongodb does not work on HHVM currently, skipping"
+else
+  echo "extension = mongo.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini
+fi
 
 # enable text search
 mongo --eval 'db.adminCommand( { setParameter: true, textSearchEnabled : true})'